Jorge,
DRM errors happen for numerous reasons.
I'd suggest opening a support case and we can analyze the error, plus using the technotes on http://www.adobe.com/support/digitaleditions/.
To open a Digital Editions 1.5 Technical Support case, please use the contact links at http://www.adobe.com/support/digitaleditions.
Regards,
Bentley Wolfe
Senior Support Engineer, Flash/Flash Player/Digital Editions
Adobe